Conventionally, as an airbag control apparatus, an apparatus has been well known which detects an acceleration value caused by an impact with the use of a sensor and determines that an object collides with a vehicle when the detected acceleration value is equal to or greater than a predetermined value.
In addition, in order to prevent a false operation of an airbag when a door is closed from a door opening condition, an airbag control apparatus has been well known which does not operate the airbag by determining a threshold value based on an impact generated by a normal door closing operation.
In addition, an apparatus has been known. The apparatus provides a door opening or closing condition detecting unit and prohibits an airbag operation for a predetermined period after closing a door when the door opening or closing condition detecting unit has detected that the door has been closed, even if an acceleration sensor detects an acceleration value equal to or greater than a predetermined value (for example, see Patent Document 1).    [Patent document 1] Japanese Patent No. 3095920
In a conventional system which prevents a false operation of an airbag when a door is closed from a door opening condition, a threshold value is determined based on an impact on the vehicle when the door is closed in a case where a vehicle is horizontally positioned. However, actually, in many cases, a door is closed in a condition where a vehicle is inclined toward a right, left, front, or rear side relative to the horizontal direction due to an inclination of a road or a parking lot.
FIG. 1 is a diagram showing impacts (forces) on a vehicle when a door of the vehicle is closed in cases where the vehicle is positioned in a horizontal condition or an inclined condition. As shown in a lower part of FIG. 1, when a left side door is closed in a condition where the vehicle inclines toward the right side viewed from a driver of the vehicle, a door closing force becomes a force in which a door's own weight is added to a normal door closing force which is applied to the vehicle when the vehicle is horizontally positioned shown in an upper part of FIG. 1. That is, in the upper part of FIG. 1, when the vehicle is horizontally poisoned, only the normal door closing force (a conventionally assumed force) is applied to the vehicle; however, in the lower part of FIG. 1, a force greater that the conventionally assumed force is applied to the vehicle.
Therefore, even if the left side door is closed by the same force as the force in the condition where the vehicle is horizontally positioned, the left side door is closed with a velocity higher than a normal velocity in the inclined condition of the vehicle, and a force greater than an assumed force is applied to the vehicle. In this case, an impact greater than an assumed impact for determining a threshold value to operate the airbag is generated, and there is a risk that a false operation of the airbag occurs. On the other hand, when the threshold value is determined to be a high value to prevent the false operation of the airbag, the airbag may not be operated when an airbag operation is actually required.